The present invention relates to a tucker cylinder for use in a sheet-folding apparatus.
The general construction and mode of operation of sheet folders is well-known. These folders generally comprise one or more pairs of cylinders which are rotated about parallel axes and on which the folding takes place. A sheet of paper is engaged by a gripper or the like on a first cylinder and thereafter a tucker blade on the same cylinder inserts the sheet into a jaw on the second cylinder to form a fold. The jaw on the second cylinder closes onto the fold and the gripper on the first cylinder releases the end of the sheet. The folded sheet is released from the jaw to be conveyed into a stacker, a collater or other depository.
In some tucker mechanisms the tucker blade extends radially outward from the first cylinder. It may be fixed or it may move radially in and out at the proper time. Difficulties have been encountered with this type of mechanism because the tucker blade tends to pull the sheet out of the jaw of the second cylinder. The cylinder rotates. This is caused by the fact that the angle which the tucker blade on the first cylinder makes with jaws in the second cylinder changes as the pair of cylinders rotate so that the tucker blade at the time of withdrawal may be at a substantial angle to the opening formed by the jaw in the second cylinder. As the tucker blade is withdrawn at this steep angle it may tend to pull the sheet along with it and thus interrupt the folding operation.
These difficulties may be overcome in part by mounting the tucker blade to move radially with respect to the first cylinder but having the tucker blade itself disposed at a fixed angle with respect to the radius of the first cylinder. This, however, does not entirely solve the problem since under these conditions the tucker blade enters the jaw of the second cylinder at a steeper angle than before, and upon withdrawal it may still cause the folding machine to jam, especially when the paper must be inserted relatively deeply into the jaw.
Because of these difficulties considerable effort has been directed toward controlling the movement of the tucker blade. The motion of the tucker blade has been controlled by various types of cams and linkages so that it forms a substantially constant angle with the gap defined by the jaw of the second cylinder during the time that the sheet is being inserted by the tucker blade and the tucker blade is withdrawn. Examples of such mechanisms are found in Greiner U.S. Pat. No. 3,727,909 and Huffman U.S. Pat. No. 3,124,349.